In the last 30 days

• Open/close The anti-k_t jet clustering algorithm

  Matteo Cacciari et al  JHEP04(2008)063 Tag this article

  Article References Full text PDF (336 KB)

  The k _t and Cambridge/Aachen inclusive jet finding algorithms for hadron-hadron collisions can be seen as belonging to a broader class of sequential recombination jet algorithms, parametrised by the power of the energy scale in the distance measure. We examine some properties of a new member of this class, for which the power is negative. This ``anti- k <sub>t</sub> '' algorithm essentially behaves like an idealised cone algorithm, in that jets with only soft fragmentation are conical, active and passive areas are equal, the area anomalous dimensions are zero, the non-global logarithms are those of a rigid boundary and the Milan factor is universal. None of these properties hold for existing sequential recombination algorithms, nor for cone algorithms with split-merge steps, such as SISCone. They are however the identifying characteristics of the collinear unsafe plain ``iterative cone'' algorithm, for which the anti- k _t algorithm provides a natural, fast, infrared and collinear safe replacement.
• Open/close Tensor hierarchies of 5- and 6-dimensional field theories

  Jelle Hartong and Tomás Ortín  JHEP09(2009)039 Tag this article

  Article References Full text PDF (414 KB)

  We construct the tensor hierarchies of generic, bosonic, 5- and 6-dimensional field theories. The construction of the tensor hierarchy starts with the introduction of two tensors: the embedding tensor which tells us which vector is used for gauging and another tensor Z which tells us which vector is eaten by a 2-form. In dimensions d ≥ 5 these two (deformation) tensors are in principle unrelated. Besides and Z there can be further deformation tensors describing other couplings unrelated to (but compatible with) gauge symmetry. For each deformation tensor there appears a ( d−1)-form potential and for each constraint satisfied by the deformation tensors there appears a d-form potential in the tensor hierarchy. For each symmetry of the undeformed theory there is an associated ( d−2)-form appearing in the tensor hierarchy. Our methods easily generalize to arbitrary dimensions and we present a general construction for the d-, ( d−1)- and ( d−2)-form potentials for a tensor hierarchy in d dimensions.
• Open/close Holographic superconductors

  Sean A. Hartnoll et al  JHEP12(2008)015 Tag this article

  Article References Full text PDF (605 KB)

  It has been shown that a gravitational dual to a superconductor can be obtained by coupling anti-de Sitter gravity to a Maxwell field and charged scalar. We review our earlier analysis of this theory and extend it in two directions. First, we consider all values for the charge of the scalar field. Away from the large charge limit, backreaction on the spacetime metric is important. While the qualitative behaviour of the dual superconductor is found to be similar for all charges, in the limit of arbitrarily small charge a new type of black hole instability is found. We go on to add a perpendicular magnetic field B and obtain the London equation and magnetic penetration depth. We show that these holographic superconductors are Type II, i.e., starting in a normal phase at large B and low temperatures, they develop superconducting droplets as B is reduced.
• Open/close NLO single-top production matched with shower in POWHEG: s- and t-channel contributions

  Simone Alioli et al  JHEP09(2009)111 Tag this article

  Article References Full text PDF (1.09 MB)

  We present a next-to-leading order calculation of single-top production interfaced to Shower Monte Carlo programs, implemented according to the POWHEG method. A detailed comparison with MCatNLO and PYTHIA is carried out for several observables, for the Tevatron and LHC colliders.
• Open/close Forward jet production at the Large Hadron Collider

  M. Deak et al  JHEP09(2009)121 Tag this article

  Article References Full text PDF (270 KB)

  At the Large Hadron Collider (LHC) it will become possible for the first time to investigate experimentally the forward region in hadron-hadron collisions via high- p _T processes. In the LHC forward kinematics QCD logarithmic corrections in the hard transverse momentum and in the large rapidity interval may both be quantitatively significant. We analyze the hadroproduction of forward jets in the framework of QCD high-energy factorization, which allows one to resum consistently both kinds of corrections to higher orders in QCD perturbation theory. We compute the short-distance matrix elements needed to evaluate the factorization formula at fully exclusive level. We discuss numerically dynamical features of multi-gluon emission at large angle encoded in the factorizing high-energy amplitudes.
• Open/close PYTHIA 6.4 physics and manual

  Torbjörn Sjöstrand et al  JHEP05(2006)026 Tag this article

  Article References Full text PDF (4.04 MB)

  The Pythia program can be used to generate high-energy-physics `events', i.e. sets of outgoing particles produced in the interactions between two incoming particles. The objective is to provide as accurate as possible a representation of event properties in a wide range of reactions, within and beyond the Standard Model, with emphasis on those where strong interactions play a rôle, directly or indirectly, and therefore multihadronic final states are produced. The physics is then not understood well enough to give an exact description; instead the program has to be based on a combination of analytical results and various QCD-based models. This physics input is summarized here, for areas such as hard subprocesses, initial- and final-state parton showers, underlying events and beam remnants, fragmentation and decays, and much more. Furthermore, extensive information is provided on all program elements: subroutines and functions, switches and parameters, and particle and process data. This should allow the user to tailor the generation task to the topics of interest.

  The code and further information may be found on the Pythia web page: http://www.thep.lu.se/~torbjorn/Pythia.html .

• Open/close String theory and noncommutative geometry

  Nathan Seiberg and Edward Witten  JHEP09(1999)032 Tag this article

  Article References Full text PDF (995 KB)

  We extend earlier ideas about the appearance of noncommutative geometry in string theory with a nonzero B-field. We identify a limit in which the entire string dynamics is described by a minimally coupled (supersymmetric) gauge theory on a noncommutative space, and discuss the corrections away from this limit. Our analysis leads us to an equivalence between ordinary gauge fields and noncommutative gauge fields, which is realized by a change of variables that can be described explicitly. This change of variables is checked by comparing the ordinary Dirac-Born-Infeld theory with its noncommutative counterpart. We obtain a new perspective on noncommutative gauge theory on a torus, its T-duality, and Morita equivalence. We also discuss the D0/ D4 system, the relation to M-theory in DLCQ, and a possible noncommutative version of the six-dimensional (2,0) theory.

• Open/close QCD vacuum properties in a magnetic field from AdS/CFT: chiral condensate and Goldstone mass

  A.V. Zayakin  JHEP07(2008)116 Tag this article

  Article References Full text PDF (214 KB)

  Chiral condensate and η' meson mass spectrum are studied under the influence of an external Abelian magnetic field. We work within the D3/D7 Karch-Katz model of flavoured AdS/CFT with supersymmetry broken by the Constable-Myers deformation of the metric. It is shown that this setting yields an analytic (quadratic) dependence of condensate on field, typical for the Nambu-Jona-Lasinio model, rather than the non-analytic (linear in field) result, typical for chiral perturbation theory in the exact chiral limit. We conjecture that the analytic (quadratic) result might be put into correspondence with the leading-order in the 1/ N _c decomposition for the condensate. This leading order in the 1/ N _c approximation has not yet been derived from the chiral perturbation theory. Thus the dual model yields the quadratic field dependence of the condensate, which is beyond the range of feasibility of chiral perturbation theory.
• Open/close Quantum tunneling beyond semiclassical approximation

  Rabin Banerjee and Bibhas Ranjan Majhi  JHEP06(2008)095 Tag this article

  Article References Full text PDF (247 KB)

  Hawking radiation as tunneling by Hamilton-Jacobi method beyond semiclassical approximation is analysed. We compute all quantum corrections in the single particle action revealing that these are proportional to the usual semiclassical contribution. We show that a simple choice of the proportionality constants reproduces the one loop back reaction effect in the spacetime, found by conformal field theory methods, which modifies the Hawking temperature of the black hole. Using the law of black hole mechanics we give the corrections to the Bekenstein-Hawking area law following from the modified Hawking temperature. Some examples are explicitly worked out.
• Open/close Higher dimensional supersymmetry in 4D superspace

  Nima Arkani-Hamed et al  JHEP03(2002)055 Tag this article

  Article References Full text PDF (232 KB)

  We present an explicit formulation of supersymmetric Yang-Mills theories from = 5 to 10 dimensions in the familiar = 1, = 4 superspace. This provides the rules for globally supersymmetric model building with extra dimensions and in particular allows us to simply write down = 1 SUSY preserving interactions between bulk fields and fields localized on branes. We present a few applications of the formalism by way of illustration, including supersymmetric ``shining'' of bulk fields, orbifolds and localization of chiral fermions, anomaly inflow and super-Chern-Simons theories.